Compartmentalization of Decay in Trees

JW*

COMPARTMENTALIZATION

OF

DECAY

IN

TREES

\v fa***

*, •

*H2

8 v^ •

'rr*U...

Forest Service

U.S. Department of Agriculture

Agriculture Information
Bulletin No. 405

Watercolor illustrations by David M. Carroll, Warner, New Hampshire.

•&• U.S. GOVERNMENT PRINTING OFFICE : 1977 O— 231-254

For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402

COMPARTMENTALIZATION
OF DECAY IN TREES

Alex L. Shigo

Plant Pathologist, U.S. Department of Agriculture,

Forest Service, Northeastern Forest Experiment Station,

Durham, New Hampshire

and

Harold G. Marx

Research Applications Staff Assistant, U.S. Department of Agriculture,

Forest Service, Washington, D.C.

Agriculture Information
Forest Service Bulletin No 405

U.S. Department of Agriculture July 1977

INTRODUCTION

The science of tree pathology
emerged from studies on decay
almost a century ago. Many of
the concepts developed then
have changed little over the
years. But, in the last few dec-
ades some additional information
on the decay process in trees
has been developed. This new
information has added to the
basic story of decay without
subtracting anything important
from it. The new expanded
concept of decay is simply more
complete. And this new, more
complete concept gives us a
better opportunity to regulate and
control decay.

Dr. George H. Hepting made
the first sound observations on
compartmentalization of decay in
trees in 1935. His ideas acted
as a trigger for the work that
followed. The work presented
here is an expansion of his
ideas.

The information in this pub-
lication is based on 16 years of
research by Dr. Shigo that in-
volved complete dissections of
approximately 10,000 trees—
mostly deciduous hardwoods, at
least 1,000 conifers, and 17
tropical species. Details of these
studies have been published
elsewhere.

The purpose of this publication
is to show how most columns of
discolored and decayed wood
associated with trunk wounds in
trees are compartmentalized. A
great number of confusing
terms are given to a wide variety
of defects caused by discolora-
tions and decays in trees. This
book describes a system that
makes it possible for forest
managers to understand how
most of these defects develop.
To understand the system, the

report must be studied very care-
fully. The system is called
CODIT
Compartmentalization Of Decay
In Trees
When the system is learned, it
will act as the code for under-
standing a wide variety of
defects on most tree species.

The CODIT system is based on
two major points. First, a tree is
a highly compartmented plant.
Second, after a tree is wounded,
the resulting defects are
compartmentalized.

To apply the CODIT system
it is necessary to understand that
the new expanded decay concept
developed in the last few decades
includes: 1) Successions of
microorganisms associated with
discoloration and decay, and 2)
Compartmentalization of dis-
colored and decayed wood
associated with trunk wounds.

To begin with, decay of wood
is a natural process caused by
microorganisms, mainly fungi,
that enter trees through wounds.
Tree wounds are usually inflicted
by fire, weather, insects, birds,
small or large animals, or man
and his activities. These wounds
start the processes that can lead
to decay, and decay is a major
cause of damage to trees. While
wood decay is most often caused
by decay-causing fungi, these
fungi are often intimately asso-
ciated with bacteria and non-
decay fungi in the process.
Decay is the breakdown or de-
composition of dead organic
matter. It is also essential to
new life.

To understand how trees react
to wounding and the associated
defects by compartmentalizing
the defects, it is necessary to
reevaluate our concept of how
a tree is constructed. A tree is
considered here as a highly

compartmented plant. In a sense,
a tree is made up of many trees;
each growth ring is a "tree."
Each "tree" is divided into many
compartments. A compartment
can be thought of as a "room,"
with side walls made up of rays
and front and back walls made
up of cells that are the last to
form in each growth ring. The
top and bottom of the compart-
ment is formed after wounding
when the elements that transport
liquids plug up. The compart-
ment is the least common de-
nominator of the tree. All the
types of cells found in the woody
stem of a tree will be found in
each compartment.

When microorganisms invade
tree stems through wounds, they
do so in successions. Bacteria,
nondecay fungi, and decay fungi
are often intimately associated
in this invasion process. When
microorganisms invade, they first
surmount the chemical protec-
tive barriers set up by the tree
and then move into the tree from
compartment to compartment.

The weakest walls of a compart-
ment are the tops and bottoms,
and the inner walls. The side
walls are fairly strong. When all
these walls fall to the invading
microorganisms, there is another
wall that begins to form. The
wall formed by the cambium
after wounding is the barrier
zone. This wall confines the in-
vasion to the wood present at the
time of wounding. The new
"trees" or rings that continue
to form are then protected from
invasion unless new wounds are
inflicted. When new wounds are
inflicted at later times, multiple
columns of defect develop.

An understanding of CODIT
will help to clarify many mis-
conceptions about decay.

Decay is a natural process.
The breakdown of dead organic
matter is essential for new
life.

Fungi are the major group of
microorganisms that decay wood
In many cases fungi accomplish
this only in association with
other organisms, especially
bacteria.

Wood-inhabiting microorgan-
isms enter trees through wounds
Wounds start the processes that
can lead to decay. And decay is
a major cause of damage to
trees.

Decay

Conifers

*M

.?-..

.Sound heartwood

Well-healed
.branch stubs

No large wounds

High-quality
pine developing

c

Deciduous hardwoods and
tropical trees

Poorly healed

Well-Healed
.branch stubs

Clear, sound

sapwood

No heartwood

~xBigh-qua!ity

branch stub

Central column
of discolored wood

Open wound

mapfe developing

ity n>
developing

Some common wounding agents
are

a-w-f

X/'

/

~>

1

Birds

Large animals

*1Al ' <*

But, before explaining how

wounds start the decay process,
'- it/s necessary to understand
... it»ow a tree is constructed. A tree

is a highly compartmented planar, v* • v
. Trees do not replace injured

tissues as animals do. T
"^compartmentalize injured tiss

»**V 'J

y*'\S~

A tree is a
- compartmented plant

ttrT>Crm-i! •/•»/■,

10

Diagrammatic
drawing
of a tree.

'tree

In a sense, a tree is made up
of many trees. Each growth ring
can be thought of as a separate
tree.

x

^

Pith

Ray cells form side walls of
compartments. 3

Last cells to form in growth ring
form inner walls of compartment.

2

In a diagrammatic way, here
is how a tree is constructed.
(The drawings are designed to
give a general impression of
compartments in trees and they
are not intended as technical
anatomical descriptions of cell
types and arrangements.)

The rays define the side walls
of the compartments. The last
few series of cells in the growth
ring define the inner walls. The
compartment has holes in the
top and bottom walls because
the flow of materials is main-
tained in a vertical direction.
But, one of the first events that
happens after wounding is a
plugging of this system above
and below the injury. Complete
tops and bottoms then begin to
develop on the compartments.
(The term "walls" is used here
in a very loose sense only to
give the mental impression of
"rooms" or compartments in
the tree.)

/

Top and bottom of compartment
form when vertical elements plug
after wounding. 1

Compartment

12

In wood present at the time of
wounding, the tops and bottoms
of the compartments are the
weakest walls. These we will call
Wall 1. The inner walls are the
second in weakness— Wall 2. The
side walls are fairly strong-
Wall 3. The strongest wall is the
one formed by the cambium
after wounding— Wall 4.

Wall 1 is incomplete in living
sapwood because the conduct-
ing elements— vessels, tracheids
—conduct liquids in a vertical
direction. But as heartwood
forms, or after wounds are
inflicted, pits close or the con-

ducting elements are plugged.
The rate and degree of pit closure
and element plugging depend on
many factors. Completion of
Wall 1 is the result of a dynamic
process. The plugging will then
set the limits for the vertical
extension of each compartment.
When plugging occurs rapidly,
short compartments form, but
when plugging is slow, long
compartments form.

Wall 2 is continuous around
every growth ring, and from the
top to bottom of the tree.

Wall 3 is discontinuous be-
cause sheets of ray cells are not
continuous radially and longi-
tudinally throughout the tree.

Wall 4 is a much stronger,
more localized version of Wall 2.
The area— longitudinal, tangential
—covered by Wall 4 will depend
on many factors: Wound size,
type, position, severity, time of
year when wounding occurs,
and intrinsic genetic potential
to respond to wounds.

Wall 2 is continuous around growth
ring and from top to bottom of the
tree.

Compartment

Side Walls 3 are the strongest walls.
Present at time of wounding.

Inner Walls 2 are the next weakest
walls.

Wall 1 is incomplete until heartwood
forms or after wounding. It is not
planar.

Top and bottom Walls 1 are the
weakest walls.

Wall 3 is discontinuous.

Sheets of ray cells may end abruptly

both radially and longitudinally.

Each growth ring is made up of
many compartments.

13

Walls 2 are continuous around the
rings and from top to bottom.

A compartment

Wall 1 is incomplete until after
wounding

Walls 3 are discontinuous inward and
up and down.

j;

\\

^%k

*

A compartment

Vascular elements plug after
wounding and complete Wall 1.

14

Discontinuous Walls 3

Continuous Walls 2

Each growth ring is made up of
many compartments.

A tree is a highly compartmented
plant.

Discontinuous Walls 3

Continuous Walls 2

15

Sectio i

■Section B

ection B

Barrier zone

10-year old wound on maple

Barrier zone Wall 4 formed after
wounding

After wounding, the cambium
forms Wall 4. This wall is called
a barrier zone. It separates wood
formed before wounding from
wood that forms after wounding.

Color key to all drawings

RED — Host response to wounding,
chemical reactions to STOP
invasion.

GREEN — Invasion processes by
microorganisms GO through the
barriers set up by the tree.

BLUE — Infection of dead and dying
tissues on wound surface.

BROWN — Decay processes.

16

Pp3k

?of

bottom
compartment

Q^ner^WaM^2j

Bark

Section B

Bark

I:

1—

4—

■Top and bottom walls are weakest walls
■Barrier zone equals strongest wall

2 — Inner wall 3 — Ray wall

17

Deep

experimental
drill wound

Host
response

Maple

After wounding, the tree
reacts. Chemical barriers de-
velop around the injured tissues.
Some wood-inhabiting micro-
organisms surmount these
barriers and begin to interact
with the tree. The tree exerts a
living protective force to keep the
invaders out. and the invaders
exert a strong force to get into
the tree through the wound.
When microorganisms are able
to get in, they move from com-
partment to compartment. And

when the walls of the compart-
ments begin to fall to the force
of the invaders, the tops and
bottoms (Wall 1) go first, then
the inner walls (Wall 2), and
then the side walls (Wall 3). But,
most of the time the barrier zone
(Wall 4) holds, and confines the
invaders to the wood present at
the time of wounding. The
figures 1, 2, 3, and 4, in addi-
tion to naming the wall, also
indicate the relative strength of
each wall. It must be emphasized

that the walls are not absolute
in their compartmentalizing
capacities and given enough
time, even the barrier zone
(Wall 4) will fall.

18

Diameter of tree
at time of wounding

/ \

1 1 fiHji Ijlijil'! Hi-

Wood formed
after wounding

10-year-old wound

Barrier zone Wall 4

Wall— 1 Weakest
—2
—3
— 4 Strongest

19

uA

Red maple

The type, severity, and posi-
tion of the wound will affect the
extent of compartmentalization.
Here are some of the most
typical examples.

Barrier zone
Wall 4

20

Three severe basal wounds.
All inner compartment walls have
fallen and only the barrier zone
remains. This is how hollows
develop.

Barrier zone Wall 4

>\

21

Dark
discoloration

A basal wound of moderate
severity. The entire "group of
trees" present at the time of
wounding was altered slightly,
and were confined by the
barrier zone. The side walls, or
rays, held here and the column
was wedge-shaped in cross-
section. The jagged vertical edge
was due to variation in confining
ability of compartment tops and
bottoms in different growth
rings.

22

A slight basal wound. The
entire column of wood present
at the time of wounding was
altered very little, but it was
still confined by the barrier zone.
The inner walls and side walls
held firm here and only a
"moon ring" formed.

Very faint
discoloration

Diameter of tree
when wounded

23

In general, the same types of
columns occur in trees that have
a heartwood core. Discolored
and decayed wood is compart-
mentalized in heartwood. When
a mechanical wound penetrates
the sapwood to the heartwood,
the column develops most
rapidly along the sapwood-
heartwood boundary.

Heartwood

Heartwood

Sapwood

Sapwood

Wound

Young red oak

24

RED — Host response to wounding
BLUE — Surface infection
GREEN — Discoloration
BROWN — Decay
YELLOW — Heartwood

Injured cambium

Injured cambium

Host response

njured cambium

25

Heartwood formation stalled near
wound.

Barrier zone in heartwood

26

Young oak

Wsumfl/ rfp_

Injured cambium

Large broken
branches

Discolored and decayed wood
associated with poorly healed
large branch stubs is compart-
mentalized in heartwood. Central
columns of defect in heartwood-
forming trees are often asso-
ciated with poorly healed
branch stubs.

Decay

27

Here are the basic patterns of
compartmentalized columns of
discolored and decayed wood
associated with a single wound
and with several wounds at one
time shown on cross section
in nonheartwood-forming
trees.

28

Here are some basic patterns
for heartwood-forming trees.

Discolored
heartwood

Slightly
altered
heartwood

Ira ..

29

Injured
cambium

Injured
cambium

Large

broken

branch

Most trees receive many
wounds during their lives. Every
tree has some branches that
die. When the branches are
small and the wounds close
rapidly, very little internal defect
follows. But, when large branches
die and healing is slow, trouble
starts for the tree. Add to this
the injuries caused by other
types of wounds at irregular
time intervals and a pattern of
multiple columns begins to de-
velop. But again the tree com-
partmentalizes the injuries and
each column is separated
from the others.

30

*% Wound

Injured cambium, new barrier zone
forming

Injured
cambium

31

Wound

Old barrier
zone Wall 4

New barrier
zone forming

Old barrier
zone

32

20-ye.

30-year-old branch stub wounds

r»rr\oajcrfl( iff^

33

>J

Open branch stub-

Barrier zone Wall 4

A

Open branch stub

Diameter
when first
wounded

New column of defect
does not move into
old central column.

Multiple columns are common
in trees. A minor wound may set
up a central column of discolored
wood and later large branches
die and heal slowly. The decay
associated with the branch stubs
does not penetrate the inner
column of compartmentalized
discolored wood.

Wound

34

A central column of compart-
mentalized discolored wood may
be associated with large branch
stubs that healed slowly, but
did close before decay set in.
Additional columns of discolored
and decayed wood could develop
later, for example, from severe
mechanical wounds on the
trunk.

Wound

Barrier zone
Wall 4

Stub

35

Here are some typical patterns
of multiple columns found in
nonheartwood-forming trees.

4 4 4

. If'

mum ^'

■

36

In heartwood -forming trees the
patterns are the same, but they
are sometimes difficult to see
because they are often contained
in heartwood that is already
dark in color. Compartmentali-
zation explains how columns
of discolored and decayed wood
can be found in ring patterns
separated by sound wood.

4 4 4

U LL \

w

Many
columrtsAk '»

>

»

m

Pmc lM*tl kui* i \ f

37

A major obstacle in understand-
ing multiple columns of com-
partmentalized decay is the
difficulty in "seeing" them in
three dimensions.

Here are some examples:

Birch— Column of discoloration

and decay associated with
a wound developing
around a central column
of discoloration associated
with branch stubs.

Stub

Old wound

Barrier zone

Central column
of discolored wood

38

Maple— Column of discoloration
and decay associated
with a wound developing
around a central column
of discoloration. The
entire column of wood
present at the time of
wounding has been
altered slightly. When
this wood is dried, it
will be a different shade
from the wood that
formed after wounding.

Wood altered slightly

Central column of
discolored wood

Wound

Barrier zone

39

Pine— Column of discolored and
decayed wood associated
with a wound developing
around a central column
of discolored heartwood
associated with poorly
healed branch stubs.

Barrier zone

Wound

Central column of discolored
heartwood

Sapwood

Heartwood

40

Ash— Column of discolored and
decayed wood associated
with a wound developing
around a central column of
decay associated with old,
poorly healed branch stubs.
The barrier zone is the
ring shake boundary.

Barrier zone

Ring shake
along
barrier zone

Wound

mtcartH IPS

41

Slightly altered columns of com-
partmentalized wood associated
with wounds in pines are some-
times difficult to see. Some
ring patterns of defects in pine
form when mechanical wounds
are inflicted on trees that already
have discolored heartwood.

Decay is most advanced along
heartwood -sapwood Dejundary. i

Wound

Heartwood
formation stalled.

| j| envamH rtfi

42

Another explanation for ring rots
in pine and related genera is
that some of the decay fungi,
such as Fomes pini, first get
established in the center of the
trunk through branch infections.
After establishment, new columns
of decay form at the boundaries
of the sapwood and heartwood.
The new columns are compart-
mentalized and appear as
rings.

43

Old top

Sporophore

■A)-

Fomes pini

44

Heart wood
Discolored heartwood

Sporophore of
Fomes pini

New column of defect not in
sapwood

Sporo

45

The "holding power" of columns
of discolored wood can be shown
by wounds that penetrate the
columns. The new column that
forms remains separate from
the inner columns. When the
second wound is severe, decay
may develop in the new column.
This occurs in nonheartwood-
forming trees.

New barrier
zone Wall 4

Deep drill wound into sapwood and
established central column of
discolored wood

Injured Individual column in each growth

cambium ring

Discolored
column

Nonheartwood-forming tree

46

Decay did not penetrate discolored
column.

I *t>Tc3STTP) T72

47

And in heartwood-forming trees.

Deep drill wound penetrates
sapwood, heartwood, and central
column of discolored heartwood.

Injured
cambium _

bTKxuTtfi rr?^

When new wounds penetrate old
columns of decay, the decay
process proceeds rapidly in the
new column.

-■A *»0£

48

'>"KztTX>ll r/yz.

49

There are some patterns of
defects that on first inspection
do not appear to fit the concept
of compartmentalization. How-
ever, they do. The most notable
are the defects associated with
canker rots. Canker rot fungi,
once established in a tree, keep
the wound open by slowly killing
some living tissues around the
wound. This process is the same
as re-wounding. And, when the
new wound is made, a new

column begins to develop. An
intricate pattern of multiple
columns is associated with
canker rot.

New columns form as cambium is
killed each year.

Some fungi produce sterile fungus
material.

Diameter of trunk
when branch died

Fungus kills cambium and new
wounds form.

50

mm

!

hi nmramrv rt?7

51

Ring shake zone

Barrier

Slightly

altered

wood

zone

Ring "^
shake

Slightly altered wood

— Large, old open wound

Another type of defect that does
not appear to fit the concept are
ring shakes— separation of the
wood along the rings. The prob-
lem here is that the barrier
zone associated with the wounds
often forms far beyond the
visible column of defect. The
barrier zone acts as a partition
between the wood present at
the time of wounding and the
new wood formed after. When
growth stresses or other stresses
are applied, the wood sometimes
pulls apart along the barrier
zone. Most shakes are associated
with wounds, but not all wounds
result in shakes.

Om^tnj, rjfl

52

BWGMtt ll l-J-^ \if,

And, yet another type of defect
pattern that appears not to fit
the compartmentalization concept
is the "island" pattern or streak
pattern often spoken of as
mineral streak. Wounds indeed
start these processes. A pattern
type that can be termed "palm
and fingers" develops. Near the
wound all the columns in the
individual growth ring are
coalesced to form the "palm."
As the discolored columns de-
velop vertically above and below
the wound, Walls 1, or the tops
and bottoms of the compartments
in individual growth rings, react
in different degrees to the
wound and the invading micro-
organisms. When such a "palm
and finger" column is viewed
in cross section at increasing
distances above and below the
wound, islands of defect appear.
Often, a few "fingers" will develop
far beyond all the others.

Wood formed
after wounding

53

In sugar maple, for example, the
"palm and finger" pattern is
the mineral streak pattern asso-
ciated with sugar maple borer
wounds. This insect is a major
cause of mineral streak in sugar
maple.

54

55

The yellow-bellied sapsucker (see
page 7) inflicts several types of
wound patterns on many species
of trees. In one type of wound
pattern a large wound is the
result, and the "palm and
finger" defect pattern develops.
Again, the "fingers" may extend
great distances above and below
the wound. And cross sections
of trunks made through the
"fingers" will show islands of
defect, or mineral streaks.

tw> a/?)

56

The "palm and finger" defect
pattern is also associated with
some other wounding patterns
made by the sapsuckers.

V\ n U

\ iV flijiifl

.Fingers | |
I

iS l

Sapsucker
wounds

*3»k*TTSV- f&*

«»^caArs» /},§

57

*»*»

Palm and finger

58

Sapsuckers will often wound one
area on a trunk. On paper birch
a swollen black band will form
at these sites.

Not only will discolored streaks
of the "palm and finger" pattern
develop from such wounds, but
the barrier zone that develops
after wounding may pull apart
from the inner rings to form a
complete ring shake which is
sometimes called cup shake or
loose heart.

"'A

Amcamil 'f£?

tmuartt)) rjn.

59

On some trees, such as eastern
hemlock, the yellow-bellied
sapsucker inflicts many wounds
over large areas of the trunk.

""fmrrst/ rift

j*%

60

The barrier zones that form after
wounding act as partitions be-
tween wood present at the time of
wounding and wood that forms
after wounding. When growth
stresses and other stresses
develop over long periods, the
wood may separate along the
barrier zones, and multiple ring
shakes form.

I;i. I'mM

iin\im*)i 11 $

61

The "palm and finger" pattern
of defect and barrier zones that
form shake are commonly
associated with wounds made
by larger animals such as beavers
and porcupines (see page 9 ).
When wounds are severe, Walls
1 and 2 may fall to invading
microorganisms.

•* /

i

•

?ni?/>r?3

62

Squirrels wound young, smooth-
barked trees in several genera
(see page 8 ). The typical "palm
and finger" defect pattern re-
sults. In some species these
defects are called mineral
streaks.

Bite wounds

Canker
from old
wound

63

Insects wound trees (see page
8) and small islands of defects
form. Each island of defect is
a small "palm and finger"
column. The columns usually
penetrate only to the depth of
the hole made by the insect.

Insect
hole

Tubes from
scale insect

Scale insect that lives in old insect
holes

-" «itt#fw*t'/m/t*it* -

. —j "^/jV^/AVvVxy*1******^'-* '

Insect
holes

11.

KlA \v_yt^~

Birch

N "^

64

When many insects attack a tree
at the same time, a barrier zone
may develop around the entire
tree. All the wood present at
the time of wounding will be
slightly altered. When dried, the
wood present at the time of
wounding will be a different
shade from the wood that formed
after wounding.

65

The cambium miner is a small
larva of a type of fly that eats
its way down the cambial region
of some trees. The "tracks" of
the larvae are compartmentalized
as very long narrow streaks of
discolored wood within growth
rings.

f

66

On some trees the wounds are
not visible. This is common with
small basal wounds, especially
those caused by fire when the
tree was very young and now
the healed wound is hidden by
forest litter. The barrier zone still
forms around such wounds and
often results in ring shake. Also,
the inrolled callus serves as a
weak spot on the tree that may
continue to split vertically. Addi-
tional cracks may form from
the barrier zone outward into
the wood that forms after wound-
ing. When the cross section of
a trunk with such a pattern of
internal defect is viewed above
the base, a star-shaped pattern
of cracks radiating out from
the center will be seen.

67

With some basal wounds, long
internal cracks, called seams,
form at right angles to the
wounds at the points where the
callus inrolls.

68

As these cracks continue to
enlarge and get closer to the
edge of the trunk, they may
suddenly split out to the bark.
These secondary seams will be
at right angles to the main seam.
Most large seams start from old
wounds and move outward.

frrzcintl? 1972.

69

Seams will also form from
mechanical wounds on trunks.
Once a seam begins to form,
it will usually continue to enlarge
throughout the life of the tree.

-r-r

io.>n\,f~

;

v r

i

b \

far

;./

Sn£ *

-,>,

70

f f *' * ' //*.-ll

71

In summary, the compartmental-
ization of defects in trees is a
survival system that is effective
most of the time— not all of the
time! And after the tree dies,

the powerful decay processes
continue to decompose the
wood. The decaying wood pro-
vides nourishment for a wide
variety of organisms.

• . / iff

72

The decomposed wood provides
nourishment for new trees.

73